1. Technical Field of the Invention
The present invention relates generally to a motor-driven swing unit such as a pan-tilt camera mount designed to remotely control panning and tilting operations of pan and tilt mechanisms for orienting, for example, an image-capturing device such as a surveillance camera vertically and horizontally, and more particularly to an improved structure of a motor-driven swing unit capable of swinging a camera horizontally over a 360xc2x0 range.
2. Background Art
Japanese Patent First Publication No. 9-284612 discloses an endlessely swingable motor-driven camera mount. FIG. 6 shows a conventional motor-driven camera mount of such a type. A camera 1 is mounted rotatably on a pan frame 3 through a tilt shaft 2. The tilt shaft 2 is connected to a tilt motor (not shown) through a gear train (not shown) and works to change a vertical angle of the camera 1 in a tilting operation.
The pan frame 3 is installed on a pan shaft 4. The pan shaft 4 is rotated by a pan motor (not shown) through a gear train (not shown) and works to change a horizontal angle of the camera 1 in a panning operation.
A bearing housing 5 has disposed therein bearings 6 which support the pan shaft 4 rotatably and is fixed on a fixture frame 7 which fixes the whole of the camera mount on the ceiling. A semitransparent dome cover 8 shields the camera 1, the tilt shaft 2, and the pan frame 3 for the purpose of presenting a fine appearance.
The camera mount also includes a slip ring transmitting unit. The slip ring transmitting unit consists of an insulating ring 9, conductive rings 10, and conductive contacts 11. The insulating ring 9 is installed on the periphery of an end portion of the pan shaft 4 projecting from the bearing 6. The conductive rings 10 are rotated by the pan shaft 4 through the insulating ring 9. The conductive contacts 11 are installed in a holder 12 secured on the bearing housing 5 through an insulating plate 13 in contact with the conductive rings 10. The slip ring transmitting unit works to establish transmission of power and control signals between a stationary assembly consisting of the bearing housing 5 and the fixture frame 7 and a swinging assembly consisting of the pan frame 3 and the pan shaft 4.
The camera mount also includes an optical signal transmitting unit which consists of a light-emitting element 14 and a light-sensitive element 15. The light-emitting element 14 is disposed within an end of a chamber of the pan shaft 4. The light-sensitive element 15 is mounted on the holder 12 and faces the light-emitting element 14. The optical signal transmitting unit converts an optical signal outputted from the light-emitting element 14 representing an image captured by the camera 1 to an electric signal. Specifically, the optical signal transmitting unit works to transmit an image signal from the swinging assembly to the stationary assembly.
The above motor-driven camera mount, however, has the following drawback. The motor-driven camera mount, as described above, has disposed therein the gear trains and stores therein grease for lubrication of the gear trains and elimination of mechanical noises, but oil contained in the grease is evaporated by a rise in inside temperature of the camera mount resulting from running of the pan and tilt motors, which results in formation of rarefied oil mist. The oil mist will stick to the surfaces of the inside parts of the camera mount to form oil films thereon. For example, they are formed on slidable electric contact surfaces of the slip ring transmitting unit and outer surfaces of the light-emitting element 14 and the light-sensitive element 15 of the optical signal transmitting unit The oil films usually absorb dust and lead to a failure of electric contacts between the conductive contacts 11 and the conductive rings 10 of the slip ring transmitting unit and cause the light sensitivity of the light-sensitive element 15 and the amount of light outputted from the light-emitting element 14 to be reduced, thus resulting in a decreased quality of the image signal.
Further, the slip ring transmitting unit is located above the bearing 5, so that the overall length of the camera mount will be greater than sum of an axial interval between the bearings 5 and a vertical length of the slip ring transmitting unit, thus resulting in an increased size of the camera mount.
It is therefore a principal object of the invention to avoid the disadvantages of the prior art.
It is another object of the invention to provide a motor-driven swing unit which has a small size, but is capable of keeping the reliability for a long time.
According to one aspect of the invention, there is provided a motor-driven swing unit which comprises: (a) a swing mechanism including a stationary housing and a rotary member disposed within the housing in connection with a device which requires motion control, the swing mechanism swinging the device through the rotary member; (b) a transmitting unit including a plurality of conductive rings and a plurality of conductive contacts, each of the conductive rings being mounted on one of the rotary member and the stationary housing of the swing mechanism in electrical contact with one of the conductive contacts to establish transmission of at least one of required electric power and a required signal therebetween; (c) an optical signal transmitting unit including a light-emitting element and a light-sensitive element separated physically from the light-emitting element, one of the light-emitting element and the light-sensitive element being attached to a portion of the rotary member in optical alignment of the light-emitting element and the light-sensitive element with an axis of rotation of the rotary member so as to establish transmission of an optical signal from the light-emitting element to the light-sensitive element for transmitting data to or from the device; and (d) a hermetic chamber defined within the housing of the swing mechanism, the hermetic chamber having disposed therein the transmitting unit and the optical signal transmitting unit.
In the preferred mode of the invention, a signal processing circuit is further provided which processes an output of the light-sensitive element produced by the optical signal from the light-emitting element. The signal processing circuit includes an AGC amplifier controlling a gain of the output of the light-sensitive element.
The signal processing circuit may also include a frequency compensation circuit for compensating for a frequency of the output of the light-sensitive element.
The hermetic chamber may be filled with inert gas.
The swing mechanism also includes two bearings disposed within the housing at a given interval away from each other in alignment with the axis of rotation of the rotary member for supporting the rotary member rotatably. The hermetic chamber is made up of a first and a second closed chamber. The first closed chamber is formed by a first inner wall of the housing between the two bearings. The second closed chamber is formed by a second inner wall of the housing outside the bearings.
The swing mechanism also includes a cover installed on an open end of the housing to define the second chamber between an inner wall of the cover and a surface of one of the bearings.